"Carbohydrate loading" the night before a big race can harm your performance and your health. More than forty years ago, I reported the case of a marathon runner who had a heart attack after carbohydrate loading in the Journal of the American Medical Association (JAMA, March 26, 1973;223(13):1511-1512). A review of 88 studies shows that eating carbohydrates DURING competitions lasting longer than 70 minutes will prolong your endurance far more than anything you eat BEFORE a competition. The longer the event, the greater the benefit of eating during competitions (Sports Medicine (Auckland, NZ), September 2011;41(9):773-92).

How Did Carbohydrate Loading Get Started?
First proposed in 1939, the carbohydrate loading regimen was supposed to increase the amount of sugar stored in your muscles before a race or endurance competition. The process took several days: a four-day depletion phase and a three-day loading phase.
• Seven days before a competition: Exercise for several hours to deplete your muscles of their stored sugar supply (glycogen).
• Sx to four days before competition: Keep your muscles empty of sugar by severely restricting all carbohydrates (sugar, fruits, flour, bakery products, pasta and so forth)
• Three to one days before competition: Eat your regular meals with lots of extra carbohydrates including bakery products and pastas.
• The night before competition: Eat a huge high-carbohydrate meal of pasta and bakery products.

We now know that the theory was wrong because your muscles can only store a very limited amount of sugar and all extra carbohydrates are immediately stored as fat. When you load up on refined carbohydrates such as bakery products, pastas and potatoes before a competition, you just become fatter. All the extra fat that forms will cause you to carry extra weight and slow you down during your race. If you already store too much fat, this overloading can make you diabetic or even suffer a heart attack. If you already have blocked arteries leading to your heart, you can kill yourself by loading with sugar or flour for just one meal.

How Carbohydrate Loading Can Harm
When you take in a lot of refined carbohydrates, your blood sugar rises. The first extra sugar is stored in your muscles and liver, but they only hold a meager amount. The liver then converts the extra blood sugar to a fat called triglycerides. A high rise in blood fat can cause clots, so much of the fat is immediately removed from your bloodstream. It is stored in fat cells, which makes you fatter, or in your liver. Fat in your liver drives blood sugar levels even higher. High blood sugar levels can cause inflammation, which can break plaques off from the inner lining of your arteries. This can block blood flow to the heart and cause a heart attack.

You Only Need a Little Extra Sugar
The limiting factor to how fast you can move over distance is the time it takes for oxygen to get into muscles. Your muscles burn primarily sugar and fat for energy. You have an almost infinite amount of fat stored in your body, but only a small amount of sugar stored in your muscles and liver. Sugar requires less oxygen than fat does. When your muscles run out of sugar, your oxygen requirements increase and you have to slow down and even stop (Clin Physiol, 1981:1:27-42). Anything that will help you to store more sugar in your muscles will also help you to move faster for a longer period of time. A rule of thumb is that you have enough sugar stored in your muscles to last during intense exercise for about 70 minutes. Athletes do not need to worry about extra sugar unless their competitive event lasts longer than 70 minutes. Realize that only a small amount of sugar can be stored in muscles. After your muscles and liver are filled with a small amount of sugar (glycogen, all the rest of the sugar is quickly converted into fat.

How Endurance Athletes Can Maximize Sugar in Muscles
Research in the 1980s led to replacement of the old seven-day carbohydrate-loading regimen with a new three-day training program that eliminates both depletion and loading. All recent research on the subject shows that conditioned athletes can store the maximum amount of sugar in their muscles just by continuing to eat their regular diet and cutting back on the amount of training they do for three days before a competition.

The day before the race: The athlete does a very short, extremely high-intensity workout (such as a few minutes of sprinting) and then eats some extra food during the next 24 hours. This results in a 90 percent increase in muscle sugar storage. Avoid sugared drinks and sugar-added foods as these can cause high blood sugar levels that can make the athlete feel sick.

The pre-race meal: You can eat anything you want as long as it:
• can pass from your stomach before you start the race, and
• is not full of sugar.
Most athletes take their pre-race meal three to four hours before they compete. The meal should contain some protein in addition to carbohydrates, but avoid sugar-added drinks or foods. A pre-race meal could include eggs, oatmeal or other whole-grain cereals, oranges, grapefruit and other fruits, bagels and so forth.

Eating and drinking just before your race: The best time to take sugar to help you prolong your intense exercise is 30 minutes or less before you start. Taking a sugar load more than 30 minutes before competition can cause a high rise in blood sugar which, in turn, causes your pancreas to release large amounts of insulin. Then you start your race with high insulin levels that, combined with your muscles suddenly pulling large amounts of sugar from your bloodstream, can cause low blood sugar levels that can make you feel exhausted even though you have just started your race. Researchers in Scotland showed that taking a sugared drink 30 minutes before exercise allowed the subjects to exercise at 90 percent of their maximum capacity for 12 percent longer than when they took the same sugared drink two hours before exercise (International Journal of Sport Nutrition and Exercise Metabolism, November 2013). The researchers showed that taking sugar two hours before exercise does not help you to sustain intense exercise any longer than taking nothing at all. You can even take chocolate because it contains both sugar and caffeine.

Eating and drinking during competition: Athletes start to run out of their sugar stored in muscles after 70 minutes of intense competition, so you need to take sugar during endurance sports that last longer than 70 minutes (Medicine & Science in Sports & Exercise, July 2010). However, you can exercise at a relaxed pace for more than three hours without needing sugar. Caffeine can increase the rate that sugar enters muscles by more than 26 percent (Journal of Applied Physiology, June 2006), so most athletes take their sugared dinks and foods with some source of caffeine. Ordinary beverages containing both sugar and caffeine are fine; there is no need for special sports energy drinks or gels. See Caffeine Improves Endurance. Caution: on very rare occasions, caffeine can cause some susceptible people to develop irregular heartbeats.

Endurance Events That Last More than Three Hours
In endurance events lasting longer than three hours, you need carbohydrates, protein, fluid and salt. In addition to rich sources of sugar (sugared drinks, fruit, chocolate bars). You can eat heavily-salted potato chips, French fries, any sandwich of your choice, or anything else that you normally eat, as long as it does not make your stomach feel uncomfortable.

NO Sugared Drinks When You Are Not Exercising Intensely
You should take sugared drinks only during vigorous exercise and for up to an hour after you finish. Contracting muscles remove sugar from the bloodstream rapidly without needing much insulin. Taking sugared drinks when you are not exercising causes higher rises in blood sugar that increase risk for diabetes and cell damage. More on Sugared Drinks

Eat Carbohydrates and Protein to Recover Faster
You will recover faster by eating a high carbohydrate, high-protein meal within a half hour AFTER FINISHING a race or a grueling workout, but taking the same high-protein-and-carbohydrate meal before a race or intense workout does not hasten recovery (Journal of Applied Physiology, May 2009). Carbohydrates in the post-race meal cause a rise in blood sugar that causes the pancreas to release insulin. Insulin drives the protein building blocks (amino acids) in the meal into muscle cells to hasten healing from intense workouts. Muscles are extraordinarily sensitive to insulin during exercise and for up to an hour after finishing exercise, so the fastest way to recover from intense workouts and races is to eat a protein- and carbohydrate-rich meal during the last part of your workout or within an hour after you finish. You can use either plant or animal sources of protein; both contain all of the essential amino acids necessary for cell growth. Protein and Carbohydrates for Recovery

Minerals
The only mineral that you need during long endurance events is salt. The food you eat will supply all the potassium, calcium, and magnesium you need. You should eat salty foods during and after you finish long rides and races. More on Salt

No Advantage to Restricting Sugar During Intense Training
The question had been asked whether restricting sugar during training could enhance performance by teaching the muscles to get along with less sugar. The enzymes used to convert sugar and fat to energy function just as well when sugar is taken continuously during exercise. A study from Copenhagen, Denmark shows that taking sugar while you exercise increases the amount of training you can do, and does not lessen the benefits of your increased training (Journal of Applied Physiology, June 2009). In this study, men trained one leg while ingesting a 6 percent sugar drink and the other leg while taking an artificially sweetened (sugarless) drink, two hours a day, on alternate days, five days a week. The legs trained with sugar had 14 percent more power and a 30 percent greater time to exhaustion. The muscles trained on sugar have no loss in the amount of stored sugar or the ability to convert food to energy.

About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities.
Read More